﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

//
// csc wsserver.cs
// wsserver.exe    
using System.Net;
using System.Net.Sockets;
using System.Text.RegularExpressions;

namespace WebSocketServer
{
    class WebSocketServer_1
    {
        private int mask;
        private int msglen;
        private int offset;

        public WebSocketServer_1(string ip = "127.0.0.1", int port = 80)
        {
            TcpListener server = new TcpListener(IPAddress.Parse(ip), port);
            server.Start();
            Console.WriteLine("Server has started on {0}:{1}, Waiting for a connection...{2}", ip, port, Environment.NewLine);


            Console.WriteLine("A client connected.");
            TcpClient client = server.AcceptTcpClient();
            NetworkStream stream = client.GetStream();

            // enter to an infinite cycle to be able to handle every change in stream
            while (true)
            {
                while (!stream.DataAvailable) ;
                while (client.Available < 3)
                {
                    // wait for enough bytes to be available
                };

                // match against "get" 
                byte[] bytes = new byte[client.Available];
                stream.Read(bytes, 0, client.Available);
                string msg = Encoding.UTF8.GetString(bytes);

                if (Regex.IsMatch(msg, "^GET", RegexOptions.IgnoreCase))
                {
                    Console.WriteLine("=====Handshaking from client=====\n{0}", msg);

                    // 1. Obtain the value of the "Sec-WebSocket-Key" request header without any leading or trailing whitespace
                    // 2. Concatenate it with "258EAFA5-E914-47DA-95CA-C5AB0DC85B11" (a special GUID specified by RFC 6455)
                    // 3. Compute SHA-1 and Base64 hash of the new value
                    // 4. Write the hash back as the value of "Sec-WebSocket-Accept" response header in an HTTP response
                    string swk = Regex.Match(msg, "Sec-WebSocket-Key: (.*)").Groups[1].Value.Trim();
                    string swka = swk + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
                    byte[] swkaSha1 = System.Security.Cryptography.SHA1.Create().ComputeHash(Encoding.UTF8.GetBytes(swka));
                    string swkaSha1Base64 = Convert.ToBase64String(swkaSha1);

                    Console.WriteLine("=====Handshaking from client key=====\n{0}", swk);

                    // HTTP/1.1 defines the sequence CR LF as the end-of-line marker
                    byte[] response = Encoding.UTF8.GetBytes(
                        "HTTP/1.1 101 Switching Protocols\r\n" +
                        "Connection: Upgrade\r\n" +
                        "Upgrade: websocket\r\n" +
                        "Sec-WebSocket-Accept: " + swkaSha1Base64 + "\r\n\r\n");

                    Console.WriteLine("=====Response from server=====\n{0}", swkaSha1Base64);

                    stream.Write(response, 0, response.Length);
                }
                else
                {
                    bool fin = (bytes[0] & 0x80) != 0;
                    bool mask = (bytes[1] & 0x80) != 0; // must be true, "All messages from the client to the server have this bit set"

                    int opcode = bytes[0] & 0xff, // expecting 1 - text message
                    msglen = bytes[1] - 128; // & 0111 1111
                    offset = 2;

                    if (msglen == 126)
                    {
                        // was ToUInt16(bytes, offset) but the result is incorrect
                        msglen = BitConverter.ToUInt16(new byte[] { bytes[3], bytes[2] }, 0);
                        offset = 4;
                    }
                    else if (msglen == 127)
                    {
                        Console.WriteLine("TODO: msglen == 127, needs qword to store msglen");
                        // i don't really know the byte order, please edit this
                        // msglen = BitConverter.ToUInt64(new byte[] { bytes[5], bytes[4], bytes[3], bytes[2], bytes[9], bytes[8], bytes[7], bytes[6] }, 0);
                        // offset = 10;
                    }

                    if (msglen == 0)
                        Console.WriteLine("msglen == 0");
                    else if (mask)
                    {
                        byte[] decoded = new byte[msglen];
                        byte[] masks = new byte[4] { bytes[offset], bytes[offset + 1], bytes[offset + 2], bytes[offset + 3] };
                        offset += 4;

                        for (int i = 0; i < msglen; ++i)
                            decoded[i] = (byte)(bytes[offset + i] ^ masks[i % 4]);

                        string text = Encoding.UTF8.GetString(decoded);
                        Console.WriteLine("{0}", text);


                        //byte[] response = Encoding.UTF8.GetBytes(text);
                        //stream.Write(response, 0, response.Length);
                    }
                    else
                        Console.WriteLine("mask bit not set");

                    Console.WriteLine();
                }
            }
        }
    }
}



